Structure and dynamics of Mercury's interior from a new generation of space-geodetic observations
Final Report Abstract
The main goal of the project Structure and dynamics of Mercury's interior from a new generation of space-geodetic observations was to make use of new data obtained from the NASA mission MESSENGER (MErcury Surface Space ENvironment Geochemistry and Ranging, messenger.jhuapl.edu) in order to advance the knowledge of the structure, dynamics, and evolution of the interior of the planet Mercury. After three flybys, MESSENGER entered into orbit on March 18, 2011. The mission, whose original duration was repeatedly extended because of its highly successful science return, is expected to end in spring 2015 when the probe will inevitably impact onto Mercury's surface. During the past few years, MESSENGER has delivered a wealth of new information that has been dramatically advancing the understanding of the geological, chemical, and physical state of the innermost planet. Taking into account the latest constraints on the interior structure, surface composition, volcanic and tectonic history, we employed numerical models to simulate the thermo-chemical evolution of Mercury's interior. We were able to demonstrate that in order to match these constraints, mantle convection must have either stopped in the past or be very weak at present. As a consequence, the observed topography and gravity field cannot be explained in terms of a dynamically-active interior. We showed that a model based on the isostatic compensation of the topography associated with lateral variations of the crustal thickness is capable to explain the data at intermediate wavelengths and provides an estimate of the mean crustal thickness (35 ± 18 km). This model, however, does not explain the long-wavelength part of the spectrum of the observations, where the largest power of the signal is concentrated. We thus introduced a new model in which the variations in surface temperature caused by Mercury's peculiar orbital parameters propagate via thermal diffusion in the presently conductive or nearly-conductive mantle, thereby inducing large-scale density anomalies. The latter cause the lithosphere and crust to deform elastically and the resulting displacements of the surface and crust-mantle interface can be related to the topography and gravity field. We showed that this model can well predict the degree 2 and 4 of the topography and gravity spectra and provides an estimate of the average thickness of the elastic lithosphere at present (~ 220 km). Although the major questions that originally motivated this project could be (at least partially) answered, two important issues remain still open that can be potentially addressed using thermo-mechanical models of the planet's interior. On the one hand, understanding the role of planetary cooling on the generation of Mercury's magnetic field via compositional convection driven by core crystallization is a fundamental task for the next generation of interior evolution models. On the other hand, it will be necessary to identify appropriate physical mechanisms able to explain the part of the spectra of the topography and gravity field that our models could not account for.
Publications
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(2012). High-performance modelling in geodynamics. In Integrated Information and Computing Systems for Natural, Spatial, and Social Sciences, Claus-Peter Rueckemann (ed.), IGI Global, 324–352
Noack L. and N. Tosi
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(2012). Thermochemical convection in planetary mantles: advection methods and magma ocean overturn simulations. In Integrated Information and Computing Systems for Natural, Spatial, and Social Sciences, Claus-Peter Rueckemann (ed.), IGI Global, 302–323
Plesa A.-C., N. Tosi and Huettig C.
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(2013). An improved formulation of the incompressible Navier- Stokes equations with variable viscosity. Physics of the Earth and Planetary Interiors, 220, 11–18
Huettig C., N. Tosi and W.B. Moore
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(2013). Thermo-chemical evolution of Mercury’s interior. Journal of Geophysical Research - Planets, 118, 2474-2487
Tosi N., M. Grott, A.-C. Plesa and D. Breuer
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(2014). Evolution of planetary interiors. Encyclopedia of the Solar System (3rd Edition), T. Spohn, D. Breuer and T. Johnson (eds.), Elsevier, Ch. 9, 185–208
Tosi N., D. Breuer and T. Spohn
